React Router
Applications have more than one page…
Fulvio Corno
Luigi De Russis
Applicazioni Web I - Web Applications I - 2023/2024
Outline
• Objective and problems
• A Solution, the React way: React Router
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Full Stack React, chapter “Routing”
React Handbook, chapter “React Router”
Multi-page Single Page Applications
OBJECTIVES AND PROBLEMS
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Supporting Complex Web Applications
• Switching between many different page layouts
• Managing the flow of navigation across a set of “pages”
• Maintaining the default web navigation conventions (back, forward,
bookmarks, …)
• Allowing URLs to convey information
• Avoiding to re-load KBs of JavaScript at every page change
• Keeping the state across page changes
• …
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Example
• Different layout
and contents
/ /profilename • Some common
parts
• No “page reload”
• URL changes
accordingly
/pages/?category=your
/pagename
_pages
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Some Use Cases
• Main list / detail view
• Logged / Unlogged pages
• Sidebar navigation
• Modal content
• Main Contents vs. User Profile vs. Setting vs. …
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Using URLs for Navigation State
• URLs determine the type of the page or the section of Example URLs on
the website facebook.com:
– Changing page ⇆ Changing the URL /
/profile.name
• URLs also embed information about the item IDs,
/profile.name
referrers, categories, filters, etc. /posts/12341232124
• URLs can be shared/saved/bookmarked, and they are 22123
/pagename
sufficient for rebuilding the whole exact page
/pages/?category=y
– Deep Linking our_pages
• Back and Forward buttons navigate the URL history
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Using URLs for Navigation State
• URLs determine the type of the page or the section of Example URLs on
the website facebook.com:
– Changing page ⇆ Changing the URL /
/profile.name
• URLs also embed information about the item IDs,
/profile.name
referrers, categories, filters, etc
Special configuration:
/posts/12341232124
• URLs can be ➢ shared/saved/bookmarked, andreturn
With any URL, the React application will always theythe are 22123
same page (index.html/index.js) that will load and /pagename
sufficient formount
rebuilding the whole exact page
the same App
/pages/?category=y
– Deep Linking our_pages
➢ The URL content is then queried by the App to customize
• Back and Forward buttons navigate the URL history
the render
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https://reactrouter.com/
https://flaviocopes.com/react-router/
https://www.robinwieruch.de/react-router/
Full Stack React, chapter “Routing”
React Handbook, chapter “React Router”
React as a REST Client
THE REACT ROUTER
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React Router
• The problems associated with multi-page navigation and URL
management are usually handled by router libraries
• A JavaScript Router manages
– Modifying the location of the app (the URL)
– Determining what React components to render at a given location
• In principle, whenever the user clicks on a new URL
– We prevent the browser from fetching the next page
– We instruct the React app to switch in & out components
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React Router
• React does not contain a specific router functionality
– Different router libraries are available
– A commonly adopted one is react-router https://reactrouter.com/
• Current version 6.4 https://github.com/remix-
run/react-router
– npm install react-router-dom
• Will also install react-router as a dependency
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Features
• Connects React app navigation with the browser’s native navigation
features
• Selectively shows components according to the current routes
– Rules matching URL fragments
• Easy to integrate and understand; it uses normal React components
– Links to new pages are handled by <Link>, <NavLink>, and <Navigate>
– To determine what must be rendered we use <Route> and <Routes>
– Defines hooks useNavigate, useParams, useSearchParams
• The whole application is wrapped in a <RouterProvider> container
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Overview of React-Router
<RouterProvider> <RouterProvider >
'/about'
<Routes>
<Link to='/'>Home</Link> <Route path="/">
<Link to='/about'>About</Link> element={<Home />} />
<Link to='/dashboard'>Dashboard</Link> <Route path="/about">
element={<About />} />
<Route path="/dashboard">
element={<Dashboard />} />
</RouterProvider > </Routes>
</RouterProvider >
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Routers
• Routers can be created as functions or components
• Routers’ functions are quite new in React Router (since version 6.4)
• We will use the new Router creation functions in the course
– Also called ‘data routers’ for their additional
functionality (not used in the course)
https://reactrouter.com/en/main/routers/picking-a-router
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Types of routers
• createBrowserRouter uses normal URLs and the HTML5 Location API
– Recommended for modern browsers
– Requires some server configuration
– import { createBrowserRouter, RouterProvider } from 'react-
router-dom' ;
• createHashRouter uses ‘#’ in the URL
– Compatible with older browsers
– Requires no config on the server
– Not recommended, unless for compatibility reasons
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Types of routers
• createBrowserRouter uses normal URLs and the HTML5 Location API
– Recommended for modern browsers
– Requires some server configuration Not needed with the React Development Server.
– import { createBrowserRouter, RouterProvider } from 'react-
When served as a static bundle, all paths must be
router-dom' ; mapped to index.html:
• createHashRouter uses ‘#’ in theapp.use(express.static('build'));
URL
– Compatible with older browsers app.get('/*', function (req, res) {
– Requires no config on the server res.sendFile('build/index.html');
});
– Not recommended, unless for compatibility reasons
More on this -> next weeks!
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Creating the router -> edit main.jsx
import React from 'react'
import ReactDOM from 'react-dom/client'
import {
createBrowserRouter,
RouterProvider,
} from "react-router-dom";
import App from './App.jsx'
const router = createBrowserRouter([
{ Add the highlighted lines to
path: "/*", main.jsx
element:<App/>,
},
]);
ReactDOM.createRoot(document.getElementById('root')).render(
<React.StrictMode>
<RouterProvider router={router} />
</React.StrictMode>,
)
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https://reactrouter.com/en/main/route/route
Selective Render
• Alternative versions of a component content must be wrapped in
<Routes>
– Each alternative is represented by a Route
– The route with the “most specific” match will be rendered
• Each <Route> specifies the URL path matching requirement
– path = '/fragment' check if the URL matches the fragment
– element = {<JSXelement/>} renders the specified JSX fragment if the
path is the best match
<Routes>
<Route path="/" element={<Home/>} />
<Route path="/news" element={<NewsFeed/>} />
</Routes>
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https://reactrouter.com/en/main/route/route
Route matching Methods
• path = string matched against the URL
• A path is made of different URL ‘segments’ (separated by /)
– Static segment → e.g., users
– Dynamic segment → e.g., :userId
– Star segment → *
• Examples:
– /users/:userId
If the Location URL matches more than
– /docs/*
one route path, the most specific one is
– / selected
– /contact-us
• Options
– caseSensitive: the match becomes case-sensitive (default: insensitive)
• changing the default is not recommended
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https://reactrouter.com/en/main/route/route
Nesting Routes https://reactrouter.com/en/main/components/
outlet
• Routes may follow the layout hierarchy of the interface components
• It is possible to nest a <Route> inside another <Route> component
– The paths will be concatenated
– The parent <Routes> will browse, recursively, through all matching paths
– All route elements in the best matching path will be rendered
• The matching children will be rendered inside the <Outlet> component
in the parent’s render tree
– <Outlet> specifies “where” the matching children should be rendered
– If you forget <Outlet>, the children will not display
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Example
function App() { function Layout() {
return ( return (
<div> <div>
<h1>Basic Example</h1> <nav>... main navigation menu ...<nav>
<Routes> <hr />
<Route path="/" element={<Layout />}> <Outlet />
<Route path="about" element={<About />} /> </div>
<Route path="dashboard" );
element={<Dashboard />} /> }
</Route>
</Routes>
function About() {
</div>
return (
);
<div>
}
<h2>About</h2>
</div>
);
}
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Special Routes (1/2)
• Index route
– <Route index element={<Home />} />
– A child route with no path that renders in the parent's outlet at the parent's URL
– Use cases:
• They match when a parent route matches but none of the other children match.
• They are the default child route for a parent route.
• They render when the user doesn’t have clicked one of the items in a navigation list yet.
https://reactrouter.com/en/main/start/concepts#index-routes
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Special Routes (2/2)
• Layout route
– A route without path will always be matched
– Useful to “wrap” with a common layout its children’s routes
• “No Match” route
– Special case: path="*"
– Will match only when no other routes do
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Example
function App() { function Layout() {
return ( return (
<div> <div>
<h1>Basic Example</h1> <nav>... main navigation menu ...<nav>
<Routes> <hr />
<Route path="/" element={<Layout />}> <Outlet />
<Route index element={<Home />} /> </div>
<Route path="about" element={<About />} /> );
<Route path="dashboard" element={<Dashboard />} /> }
<Route path="*" element={<NoMatch />} />
</Route>
function Home() {
</Routes>
return (
</div>
<div>
);
<h2>Home</h2>
} </div>
);
}
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Navigation
• Changing the location URL will re-
render the Router, and all Routes
will be evaluated
• Two options:
– <Link to= > creates a router-
aware hyperlink (activated by user
clicks)
– useNavigate() returns a
function to trigger navigation
(useful inside event handlers)
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Navigation
• Changing the location URL will re- Warning
render the Router, and all Routes
will be evaluated Never use a “plain hyperlink” <a>
• Two options: Never use a “form submission”
– <Link to= > creates a router- <form action='…'>
aware hyperlink (activated by user
clicks)
– useNavigate() returns a They will reload the whole
function to trigger navigation application (and kill the current
(useful inside event handlers) state)
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Examples
function Home() { function Invoices() {
return ( const navigate = useNavigate();
<div> return (
<h1>Home</h1> <div>
<nav> <NewInvoiceForm
<Link to="/">Home</Link> onSubmit={(event) => {
{" "} const newInvoice = create(event.target);
<Link to="about">About</Link> navigate(`/invoices/${newInvoice.id}`);
</nav> }}
</div> />
); </div>
} );
}
All paths are relative,
unless they start with /
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Active Navigation
• When creating menus or navigation elements, it is useful to see which
item is the currently selected one
• <NavLink> behaves like <Link>, but knows whether it is “active”
– It adds the “active” class to the rendered link (to be customized with CSS)
– You may create a callback in className={} that receives the isActive status and
decides which class to apply
– You may create a callback in style={} that receives the isActive status and
decides which CSS style(s) to apply
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Dynamic Routes
• Routes may have parametric segments, with the :name syntax in the
path specification
– <Route path="/post/:id" element={<Post/>} />
– The ‘id’ part will be available to the element through the useParams() hook
function Post(props) {
<Route
const {id} = useParams();
path="/post/:id"
...
element={<Post/>} />
}
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Dynamic Routes
• Routes may have parametric segments, with the :name syntax in the
path specification
– <Route path="/post/:id" element={<Post/>} />
– The ‘id’ part will be available to the element through the useParams() hook
• useParams returns an object of
key/value pairs of the dynamic
params from the current URL that function Post(props) {
<Route were matched by the <Route path> const {id} = useParams();
path="/post/:id"
• Child routes inherit all params from ...
element={<Post/>} their
/> parent routes
}
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Example
function App() {
return (
<Routes>
<Route
path="/invoices/:invoiceId"
element={<Invoice />}
/>
</Routes>
); Matches a URL like
}
/invoices/1234
function Invoice() { function Invoice() {
let { invoiceId } = useParams(); let params = useParams();
return <h1>Invoice {invoiceId}</h1>; return <h1>Invoice {params.invoiceId}</h1>;
} }
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Location State: Passing Information Among Pages
• When navigating, it is possible to const navigate = useNavigate() ;
pass some information to the next // go to URL and send information
navigate( url, {state: userData} ) ;
page, thanks to the
location.state BOM attribute <Link to={url}
state={userData} >
– Alternative to dynamic URLs . . .
</Link>
• The value may be retrieved with
useLocation() on the next page const location = useLocation();
const userData = location.state;
– Beware: objects are serialized as
strings, avoid passing ‘complex’ objects
(e.g., dayjs objects)
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Exploiting Search Parameters
• A URL may contain some “query let [searchParams, setSearchParams] =
useSearchParams();
search parameters” - searchParams is a URL.searchParams object
– /products?sort=date&filter https://developer.mozilla.org/en-
US/docs/Web/API/URL/searchParams
=valid You may access each parameter with
• useSearchParams() allows searchParams.get('date')
searchParams.get('filter')
you to read and modify the query
string portion of the location - setSearchParams receives an object of { key: value }
pairs that will replace the current parameters
– Returns the current version of the
parameter, and a function to
modify them
– Behaves like useState
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Summary: react-router-dom
• Wrap main.jsx in • Parameters
createBrowserRouter – useParams() for Dynamic Routes
• Routing and rendering: – useSearchParams() for URL
– <Routes> query strings (after “?”)
– <Route path= element= /> – useLocation() for retrieving
location state (set by navigate)
– <Outlet/>
• Navigation:
– <Link to= >…</Link>
– <NavLink to= >…</NavLink>
– useNavigate() or <Navigate>
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License
• These slides are distributed under a Creative Commons license “Attribution-NonCommercial-
ShareAlike 4.0 International (CC BY-NC-SA 4.0)”
• You are free to:
– Share — copy and redistribute the material in any medium or format
– Adapt — remix, transform, and build upon the material
– The licensor cannot revoke these freedoms as long as you follow the license terms.
• Under the following terms:
– Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were
made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or
your use.
– NonCommercial — You may not use the material for commercial purposes.
– ShareAlike — If you remix, transform, or build upon the material, you must distribute your contributions
under the same license as the original.
– No additional restrictions — You may not apply legal terms or technological measures that legally restrict
others from doing anything the license permits.
• https://creativecommons.org/licenses/by-nc-sa/4.0/
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